BackgroundIn 1998, Ericsson acquired ACC as part ofits plan to reshape the company to meet thecommunication challenges of the next mil-lennium. ACC has had a long history in theearly pioneering development of theArpanet—the prolog to the Internet. SantaBarbara (ACC’s headquarters) was the siteof one of the first of four nodes to be knit-ted together, in 1969, to provide the world’sfirst packet-switched network. From thisfoundation, a team of engineers formed ACCand set about developing products to meetthe growing requirements of the university

and defense industry during the late 1970sand early 1980s.

ACC has had many networking firsts,such as advanced techniques for minimizingwide-area bandwidth costs and the intro-duction of a branch office router for underUSD 2,000. During the past two years, ACChas reshaped itself in preparation for whatit saw as confirmation that the Internet pro-tocol (IP) would become the next-generation network protocol. This new di-rection focused on the delivery of a new tech-nology platform that allows smooth andcost-effective migration from the tradition-al narrowband world of carriers into theworld of IP.

Ericsson realized that the acquisition ofACC would bolster its presence in the IPworld and provide a production-ready, carrier-class product family that would helptransition its customers into the new tele-coms world. Moreover, the acquisition waspart of Ericsson’s string-of-pearls strategy,which is designed to catapult Ericsson intothe IP world. This strategy includes the for-mation of a US-based Data Networking andIP business unit, which brings togetherEricsson’s breadth of data networking prod-ucts and skills; gives a foundation for exist-ing and new partnerships in the nascent IPworld; and gives Ericsson the ability to buildor acquire IP excellence across a range oftechnology solutions. In doing so, Ericssonpositions itself• to migrate existing wireline and wireless

customers toward IP communications;and

• to build complete end-to-end network so-lutions based on the Internet protocol.

Ericsson’s string-of-pearls strategy is con-sidered to be more innovative than similarstrategies to bolster IP competence intelecommunications companies. It providesfor selective acquisitions that target keyproduct areas, such as access, service, infra-structure and management. This strategyenables Ericsson to build a best-of-breed sta-ble of products which in themselves are su-perior to competitive products and which asa whole offer an impressive solution for end-to-end connectivity. The ACC acquisitionsupports this best-of-breed strategy—theTigris family of products was awarded the“Oscar” of the data communication indus-try, namely the 1998 Hot Product of theYear award. ACC’s IP capabilities and itsfocus on the rapidly growing access marketcomplement Ericsson’s aggressive foray intodata communications and IP.

70 Ericsson Review No. 2, 1999

In 1998, the Tigris family of products from ACC was named the data com-munication industry’s Hot Product of the Year. Ericsson’s acquisition ofACC, which was part of its string-of-pearls strategy, positions the compa-ny to migrate existing wireline and wireless customers toward IP commu-nications and to build complete end-to-end network solutions based onthe Internet protocol.

The authors describe the Tigris family, which provides a gatewaybetween circuit-switched and IP networks. Tigris’ flexible architectureallows traditional circuit-switched calls to enter or exit the world of IP. Itsbackplane provides for two bus architectures: standards-based TDM con-nectivity for more than one thousand five hundred 64 kbit/s circuit-switched connections, and a high-speed Compact PCI bus that offers upto 2 Gbit/s of bandwidth for packet-switched traffic. Combined withAccessOS software from Ericsson, this simple hybrid architecture createsa carrier-class multi-service and multi-delivery access platform.

Tigris—A gateway between circuit-switched and IP networksPeter Curtin and Bert Whyte

Road warrior

Modem

ISDN

Home user

Mobile user

PSTN

Tigris

IP backbone

Figure 1Tigris as the “bridge” between the public switched telephone network (PSTN) and the IPpacket world.

Ericsson Review No. 2, 1999 71

LandscapeIn the telecommunications industry, dras-tic change is rare. For instance, in the lastthirty years we have witnessed dramaticchange only twice: the move from analog todigital technology and the introduction ofcellular mobile technology. Ericsson identi-fied both opportunities and thereby took aworldwide leadership position. As we enterthe twenty-first century, another significantchange is taking form: the world is adapt-ing to IP technology.

The reasons for this change relate to therapid advancements in the regulatory envi-ronment spurred on by the privatization oftelecommunications monopolies around theworld. Telecommunications-related com-petition has turned impersonal “sub-scribers” of the service into valued “cus-tomers.” Existing services must be offeredat lower costs to meet competition, and newservices are being demanded to improvebusiness efficiency and to exploit thetelecommunications network as a strategictool of highly competitive global business-es. Service bundling—whereby providerspackage together both voice and data ser-vices with common delivery and billingstrategies—is another competitive tool.

Advances in technology, the rapid growthof the Internet, and next-generation com-puting power are devouring all availablebandwidth capacity, which has considerableimpact on existing wide-area networks(WAN). This growing appetite for networkbandwidth changes the rules of traditionalnetwork topologies and design. The old 80-20 rule no longer applies as users reach outacross the network for information and col-laboration. Capacity is the watchword of thenew generation of networks currently beingdesigned and implemented.

The Internet protocol provides the essentialingredient in the recipe of all future networkdesigns that will change the way we work andplay. The use of IP as the convergence agentfor linking voice, data and video into a singlecommunication stream is well understood inthe communications industry. Moreover,there are obvious economic benefits.Notwithstanding, it is the realization of “deepconvergence”—the ability of IP to transformand create new sets of communication appli-cations—that will exploit next-generationIP-based networks and provide real value tocustomers. This is the race in which we are apart as we enter the next millennium. Theplayers in this game are many, including

• the suppliers who designed and builtcommunication networks during the lasthundred years;

• the carriers who maintained and advancedthese networks;

• the new breed of vendors who offer radi-cal solutions to this new opportunity; and

• the new set of carriers who are chargedwith an entrepreneurial sense of urgencyto succeed.

Tigris concept and toplevel As illustrated in Figure 1, the Tigris fami-ly provides the gateway between circuit-switched and IP networks. Tigris’ flexiblearchitecture allows traditional circuit-switched calls, such as voice, data and fax,to enter or exit the world of IP. The back-

ADSL Asymmetrical digital subscriber lineATM Asynchronous transfer modeBGP-4 Border gateway protocol, version 4

(RFC 1771)BITS Building integrated timing systemCCITT International Telegraph and Telephone

Consultative Committee (currently theITU)

DL2 Second-generation digital linkinterface

DS3 Digital signal, level 3 (44.736 Mbit/s)DSP Digital signal processorE1 2 Mbit/s digital linkETSI European telecommunications

standards instituteGS Group switchH.323 ITU-T recommendation on visual tele-

phone systems and equipment forlocal area networks that provide anon-guaranteed quality of service

IN Intelligent networkIP Internet protocolIPX Internetwork packet exchangeISDN Integrated services digital networkISP Internet service providerL2TP Level 2 tunneling protocolLAPM Link access procedure for modemsMGCP Media gateway control protocolMNP5 Microcom networking protocol,

version 5MPLS Multiprotocol label switchingMPOA Multiprotocol over ATMMSC Mobile switching centerNAS Network access serverNEBS Network equipment building systemOC3 Optical carrier, 155 Mbit/s linkOSPF Open shortest path firstPRI Primary rate interfacePSTN Public switched telephone networkQoS Quality of service

RIP Routing information protocolRISC Reduced instruction set computerSDSL Symmetrical digital subscriber lineSIP Single in-line packageSMDS Switched multi-megabit data serviceSS7 Signaling system no. 7STM-1 Synchronous transfer module-1,

155 Mbit/s digital linkT1 1.5 Mbit/s digital linkTDM Time-division multiplexingV.100 ITU-T recommendation: Interconnec-

tion between public data networks(PDN) and the public switched tele-phone networks (PSTN)

V.21 ITU-T recommendation: 300 bit/s perduplex modem standardized for use inthe general switched telephone network

V.34 ITU-T recommendation: A modemoperating at data signaling rates of upto 33,600 bit/s for use on the generalswitched telephone network and onleased, point-to-point, two-wire tele-phone-type circuits

V.42bis ITU-T recommendation: Data com-pression procedures for data circuitterminating equipment (DCE) usingerror correction procedures

VoIP Voice over IPVPN Virtual private networkVPSM Virtual port service managerWAN Wide area networkX.25 ITU-T recommendation: Interface

between data terminal equipment(DTE) and data circuit-terminatingequipment (DCE) for terminals operat-ing in the packet mode and connect-ed to public data networks by dedi-cated circuit

xDSL Collective term for several copper-circuits-based modem technologies

BOX A, ABBREVIATIONS

plane provides for two bus architectures, astandards-based time-division multiplex-ing (TDM) connectivity for more than onethousand five hundred 64 kbit/s circuit-switched connections, and a high-speedCompact PCI bus that offers up to 2 Gbit/sof bandwidth for packet-switched traffic.This simple hybrid architecture, combinedwith AccessOS software from Ericsson, cre-ates a carrier-class multi-service and multi-delivery access platform via a range of high-density interface cards (Figure 1).

Multi-serviceBy multi-service is meant the ability to offerdifferent applications on a single platformarchitecture. In a world that is rapidly con-verging, this means the ability to supportvoice, data and video layered over IP. Theresult is the capability to offer any type ofservice over IP, including voice, fax, high-speed data, modem data, cellular data, andvideo. The industry greatly abuses the claimof being able to provide multi-service. In re-ality, very few products offer this capabili-ty. Apart from truly supporting multipleservices, the real uniqueness of the Tigrisplatform is that it does so on the fly as de-manded by users connecting into it. For ex-ample, at one instant the call on a port mayrequire traditional circuit-modem traffic tobe converted into the Internet protocol,whereas in the next moment this same portmay be asked to convert a circuit-switchedvoice call into IP. This on-the-fly adapt-ability, termed Call by call™, offers extra-ordinary flexibility to service providers whouse the Tigris platform.

In competitive offerings, ports must be sta-tically allocated to certain functions, and inmany applications these ports require dedi-cated hardware. Architectures of this kindforce network designers to over-provision configurations to cover off-peakload conditions. This results in increased cap-ital, space and operating costs. Moreover,fixed configurations do not allow for easychanges in service demands. Call by call re-moves these restrictions and enables the flex-ible usage and configuration of resources: theport supports whatever service is required.The Call by call capability, which is drivenby the number dialed, the initiator of the call,the transport indicator, or the domain nameof the caller, is tied into an intelligent net-work (IN) application called the virtual portservice manager (VPSM). This network ap-plication interrogates each call before the callis answered, to determine

• which application the connected portshould supply; and

• whether or not the call should be con-nected to the destination network (serviceauthentication and confirmation that ca-pacity is available for the requested ser-vice type).

This flexibility is coupled with the abilityto start offering users different classes of ser-vice across the Internet protocol. These dy-namic configuration options become key el-ements for service providers who provisionvirtual private networks (VPN).

The combination of Call by call and theVPSM creates a powerful tool that extendsbeyond a single Tigris to a network of Tigris.From a lone IN server (redundancy is op-tional), the service provider can instanta-neously alter the profile of select customers.For example, if a customer requests addi-tional ports for a remote-access application,the network operator can immediately in-crease the port allocation. The VPSM canalso be configured • to automatically reallocate ports to differ-

ent applications based on time of day; or• to offer premium port connectivity. The VPSM is a service tool designed to max-imize revenues by ensuring maximum portutilization, providing service differentia-tion and simplifying management and op-erational functions.

Multi-deliveryBy multi-delivery is meant the ability tooffer different network interfaces to matchthe network models in use by serviceproviders. The classical concentrator taskhas been to support only dial-in traffic, usu-ally through a T1 (1.5 Mbit/s) or E1 (2Mbit/s) primary rate interface (PRI) con-nected to the public exchange or central of-fice using integrated services digital net-work (ISDN) signaling or a form of commonchannel, such as T1 robbed bit or E1 R1/R2signaling. Tigris supports these modes andhas the added capability of supporting • leased lines—from 56 kbit/s up to digi-

tal signal level 3 (DS3, 44.736 Mbit/s);• frame relay;• X.25;• switched multi-megabit data service

(SMDS); and• asynchronous transfer mode (ATM) up to

OC3/STM-1. Work is also currently underway to inte-grate xDSL (including ADSL and SDSL)connection capability into Tigris.

From a service provider’s perspective, the

72 Ericsson Review No. 2, 1999

Ericsson Review No. 2, 1999 73

benefits of multi-delivery are obvious: a sin-gle platform that supports multiple access ser-vices enables providers to deploy Tigris in avariety of configurations supporting low-density applications that require T1/E1 con-nectivity and high-density applications thatrequire ATM connectivity. The serviceprovider can insert a variety of interfaces tooffer dial-up, high-speed, leased-line, andATM access simultaneously from the sameplatform.

IntegratedOne of the key attributes of Tigris is that itcontains every element necessary for deliv-ering connections from the circuit-switchedworld directly into the IP world. The termPOP in a Box, which is widely used in NorthAmerica, refers to products that facilitate,in a single platform, access, routing, andWAN connectivity. Architectures of thiskind appeal not only to small providers whoare concerned with capital costs but also tolarge providers who are concerned with per-formance, space and operational issues.

In this context, integrated means that theTigris is capable of many different accesstechnologies, such as modem, ISDN, cellu-lar data, voice-over-IP (VoIP) and fax. Fur-ther, integrated means that Tigris supportsa variety of routing protocols—includingthe routing information protocol (RIP),open shortest path first (OSPF), and the bor-der gateway protocol (BGP-4)—whichallow for direct connection to the Internet.

Integrated also means minimum latency astraffic passes from the circuit-switchedworld into the packet-switched world or theother way round.

It might interest the reader to know thatTigris supports complete IP and internetworkpacket exchange (IPX) routing, which con-stitutes over 99% of the wide-area routingused in service-provider and enterprise envi-ronments. You might expect other productsto have similar integrated features, but thetruth is, many of today’s networks rely on mul-tiple products to deliver the same capabilityintegrated into Tigris. In many instances,Tigris replaces up to three products needed todeliver equivalent service capability.

Understanding VPNs and the need tooffer quality of service (QoS) across a net-work is a significant pillar in Ericsson’soverall network-wide VPN architecture. Aspart of this architecture, the integration ofTigris also means a single point of controland management that facilitates the imple-mentation of service strategies.

Family of products, scalability andcarrier-class serviceAs with most things in life, one size doesnot fit every networking business need. Con-sequently, a primary requirement of theTigris design was to produce a family ofproducts. Four basic models were designed,offering different capacities and features: athree-slot, six-slot, seven-slot and eleven-slot Tigris (Figure 2).

Desktop Rackmount Chassis Non-redundant control

Redundant control

3-slot

6-slot

7-slot

11-slot

Figure 2 The Tigris family of products, and the vari-ous uses of the three-, six-, seven-, andeleven-slot Tigris.

Tigris is uniquely able to sit in a service-provider environment and still function asan enterprise access device (Figure 3). As ser-vice providers roll out their VPN offerings,consistency must be maintained at bothedges of the network. Moreover, in provid-ing this consistency, service providers mustnot only support VPN functionality but alsomulti-service delivery, class of service, andcustomer and service-provider managementcontrol.

Interestingly, the differentiation betweenenterprises and service providers is becomingmore and more diffuse. For example, in manyrespects a large corporation with the task ofproviding service to a group of telecommutersor road warriors may actually function as a ser-vice provider. That is, although the newlyformed Internet service provider (ISP) mayhave started out as a corporate enterprise thatoffered dial-up services, the business proposi-tion may have drawn them into operating likea service provider.

The requirements for enterprise and corenetwork edge products have traditionallybeen different. The Tigris architecture andphysical packaging was nevertheless de-signed to sit comfortably on each accessedge. The three- and six-slot configurationstarget the enterprise environment for thedesktop or for mounting in racks, whereasthe seven- and eleven-slot configurations aredesigned for mounting in racks in a serviceprovider environment. The three- andseven-slot configurations do not supportcontrol card redundancy; the six- andeleven-slot configurations do. This flexibil-ity enables network designers to select thechassis that best fits applications and costconstraints. Any interface card can be uti-lized in any chassis configuration, offeringmaximum flexibility, growth options, min-imum spare-part requirements and mini-mum capital investment.

Each product has undergone networkequipment building system (NEBS) level-3

74 Ericsson Review No. 2, 1999

Service providerHome user

Home user56/64 kbit/s

Local office

Mobile user

Enterprise

PBX Server farm

11-slot Tigris

3-slot Tigris

Internet

Geographically far

Geographically near

Internet access Remote sites are tunneled Remote users are tunneled VoIP calls are terminated

Remote sites on channelized T1/E1 or ISDN. Remote users on analog or ISDN.

Leased-line PSTN/ISDN

Figure 3Tigris at both edges of the access network.

Ericsson Review No. 2, 1999 75

or ETSI-equivalent testing. They are thusacceptable in harsh service-provider envi-ronments. Although not a typical enterpriserequirement, the carrier-class service fea-tures of the Tigris family provide a reliabil-ity factor not traditionally found in enter-prise equipment. This becomes more im-portant as “deep service convergence” be-comes a reality.

The carrier-class characteristics also man-date that the product can be seamlessly in-tegrated into a carrier environment. Tigriswas designed to fit comfortably into Ericsson’s BYB equipment practice. Otherfeatures that take the Tigris platforms be-yond NEBS and provide a product that isatypical of most data communication sup-pliers are • 48 volt power distribution;• on-card power conversion;• low-power design; • cooling design; • clocking options (including the building

integrated timing system, BITS); and• alarming ability.Knowing that the ultimate goal of providersis to furnish customers with massive con-nectivity, a major design objective was toprovide the ability to support high port den-sities. Simply put, we can configure moreports per Tigris than any other comparableproduct in its class. However, we have notforgotten that Tigris needs to be a family ofproducts that supports small and large in-stallations alike. To this end, Tigris sup-ports systems that scale from 24 to over2,000 ports.

Service providers and enterprises can in-stall the appropriately sized Tigris with theassurance that their investment will bemaintained as the network grows. This is animportant consideration in today’s fast-paced networking environment, wherechange and uncertainty are the norm.

Tigris in technical detailTigris was designed using open standards toprovide a highly scalable, carrier-class,multi-service delivery platform. The archi-tectural approach uses a multi-processor de-sign that distributes the various processingfunctions among general- and specific-purpose processing elements. This architec-ture ensures linear performance as the sys-tem scales from very small configurations tomaximum capacity. For example, the digi-tal signal processor (DSP) card, which is theheart of Tigris, contains both DSPs and re-

duced instruction-set computer (RISC)processors to process codecs and to handlevarious modems, compression, and packet-bus transfers.

Virtual private networks via AccessPartitions™Tigris was specifically designed to supportdial-in and dedicated access to virtual pri-vate networks, which are used by serviceproviders and corporations. On Tigris, VPNfunctionality is implemented through acombination of features collectively de-scribed as access partitioning. The VPN-based services that can be offered by serviceproviders include• wholesale Internet access; and• outsourced corporate remote access.Corporate benefits of the VPN include• guaranteed dial-in access (for important

employees or user groups); and• dial-in users routed to specific internal

corporate VPNs based on user name orcalled number.

Service profiles

Access partitioning relies on service profilesand associated access partitions to define theuser’s dial-in service. A group of called num-bers is mapped into a service profile. Cur-rently, three service types can be configuredfor a service profile:• multiprotocol bridged routing;• called number routing; and• level 2 tunneling protocol (L2TP) tun-

neling.Dial-in calls that have been configured formultiprotocol bridged routing are general-ly forwarded in accordance with the desti-nation address of the incoming dial-in pack-ets.

Service profiles provisioned for callednumber routing cause dial-in traffic to beforwarded directly• to the next-hop IP address configured for

the associated access partition; or • from the IP address returned in a

RADIUS access-reply message.Service profiles provisioned for L2TP causethe dial-in traffic to be tunneled • to the IP address that was configured for

the associated access partition; or • from the address that is returned in a

RADIUS access-reply message.Service profiles can be configured to providecalling number screening, modem pools,and access partitions.

A service profile can be configured so thata group of calling numbers is screened. Call-

ing number screening allows individual orgroups of calling numbers to be blocked orenabled. The screening action is performedbefore a call is accepted.

Modem pools

A modem pool defines a set of characteris-tics that can be configured on a digitalmodem at the time of connection. A modempool can be associated with an access parti-tion and allows the following characteristicsto be defined:• Modulation—autodetect, v.21 – v.34bis.• Maximum data rate—33.6 kbit/s, 28.8

kbit/s, and so on.• Compression—autodetect, v.42bis, MNP5,

none.• Link access procedure for modems

(LAPM) state—enabled/disabled.• Carrier detect/disconnect times.This flexibility allows for differentiated ser-vice based on maximum data rates or fast-connect times, depending on customer re-quirements.

Access partition profiles

Access partitions define the characteristicsof VPN-based service types, such as callednumber routing and L2TP. The followingcharacteristics can be defined per access par-tition:• Port limit—the total number of simulta-

neously active ports authorized for a par-tition. The port limit is checked before acall is accepted for a partition.

• Primary IP address—the called numberrouting function uses the primary IP ad-dress as the next-hop IP address when for-warding traffic. L2TP uses it as the desti-nation IP address for tunneling traffic.

• Secondary IP address—same as above. Thesecondary IP address is used when the pri-mary IP address cannot be reached.

• RADIUS proxy server—this identifies theRADIUS proxy server to be used for RADIUS authentication or accountingfor this partition (typically located at thecustomer or ISP site).

• IP address pool—this pool of IP addressesis used for dynamic assignment of IP ad-dresses to dial-in users of a specific parti-tion.

Access partition security

Access partitioning ensures that adequateseparation is maintained between individ-ual routing domains. This prevents two endstations connected to the same Tigris fromcommunicating directly. Packets received

from one ISP or corporation are also pre-vented from being inadvertently forwardedto another ISP or corporation or to a user inanother domain. Routes in one domain arenot advertised to other domains. Thus, twoend stations connected to the same Tigrisand belonging to the same routing domaincannot communicate directly. This preventsend stations from bypassing filters that maybe established at the ISP or corporation’spoint of presence.

Virtual port service managerThe virtual port service manager is a Java-based server software product designedspecifically for network service providers,enabling them to offer efficient, differenti-ated dial-in VPN services. The VPSM func-tions much like a carrier-based intelligentnetwork application but in the IP domain.It gives network service providers the abil-ity to manage dial-in services from one cen-tral point in the network. It also interactswith a network of remote access concentra-tors (that is, Tigris) using standard RADIUSmessaging during call setup and authenti-cation, to dynamically manage the alloca-tion of dial-in resources and to deliver ac-cess partitioning or VPN services.

Call management services

All registered network access servers (NAS)must query the VPSM with a called num-ber or domain name to determine whetheror not a connection can proceed. Upon re-ceiving a resolution request from the NAS,the VPSM attempts to resolve the callednumber or domain name to an access parti-tion. If the partition can accept a call, a pos-itive acknowledgment is returned to theNAS along with the access partition con-figuration. Otherwise, a negative (discon-nect) message is sent.

Resource management services

The VPSM is responsible for managing dial-in access resources in each access partitionas well as within the network. Dial-in VPNsdefined by a user name (xxx@biz.com) or bycalled numbers are configured for a network-wide quota limit that restricts—for each VPN—the total number of active,simultaneous ports. The operator has the op-tion• of refusing calls that exceed the quota; or • of accepting calls that exceed the quota—

in this case, the operator can use RADIUSto flag and charge a premium for eachoversubscribed call.

76 Ericsson Review No. 2, 1999

Ericsson Review No. 2, 1999 77

The total number of dial-in ports availableand currently in use per VPN are trackedand reported. The VPSM also manages otheradvanced services, such as priority connec-tion and guaranteed ports.

RADIUS management services

Customers may want to control and managetheir own RADIUS servers so that they canmaintain control over access to their net-works even when they have outsourced thisaccess. Proxy RADIUS is a function that al-lows the VPSM to act as a proxy to a RADIUS authentication and accountingserver. This function allows the VPSM to beintroduced confidently into networks inwhich RADIUS servers are already in placeat the customer’s site. When a user from cor-poration A dials into the carrier site, theVPSM forwards authentication and ac-counting requests to the respective RADIUS authentication or accounting serv-er located on corporation A’s network.

In another VPN application, the VPSMcan act as a proxy server for a centralized au-thentication and accounting server at thecarrier network. Carriers and ISPs that offerVPN services to corporations can use theVPSM and a central authentication and ac-counting server to maintain a central data-base with tables for each corporation. Thiseliminates the need for separate authentica-tion and accounting servers at corporatesites. Instead, user authentication and ac-counting is handled through the VPSM andRADIUS server at the carrier side.

DSP resource managementThe DSP resource interface is the heart of theTigris architecture. It is the gateway betweenthe circuit-switched and packet-switchedworlds where all modem, ISDN, V.100 fax,and voice processing occurs. The design ofthe card and the selection of DSPs was pred-icated on providing maximum density withthe least power and cooling requirements,which considerations are critical in carrierenvironments. Each DSP is dynamicallyconnected to a circuit and configured at callsetup to support the incoming call’s proto-col. This flexibility gives operators the abil-ity to support multiple call types without re-quiring them to deploy the product withdedicated hardware, fixed configurations, orboth, to support expected traffic levels.

VoIP architectureMany young technologies are accompaniedby multiple, emerging standards. Voice

over IP (VoIP) is no exception with its pro-prietary solutions, H.323, the media gate-way control protocol (MGCP) and the sin-gle in-line package (SIP). The Tigris VoIParchitecture utilizes a distributed approachto standards, separating call control from thecall-connection process. The architecture isbased on open standards utilizing the SunSolaris operating system as the basic plat-form. However, it allows for other plat-forms, such as AXE/MSC or the Tigris it-self, to support certain components. The ar-chitecture is made up of three basic compo-nents:• the signaling system no. 7 (SS7) gateway;• the media controller; and • the media gateway as well as specific

servers designed for voice- or data-application functions.

The SS7 gateway provides the interface fromthe SS7 network into the IP infrastructure.Depending on the size of the network, thisfunction can be provided by AXE/MSC, aNEBS-compliant Sun, or the Tigris.

Turku Telephone Ltd., a Finnish operator andmember of the Finnet group, was the first cus-tomer to acquire the DL2-based Tigris solution.In 1978, they hosted the first commercial instal-lation of digital AXE.

The installation consists of three identicalseven-slot Tigris connected to an AXE localexchange running the Finnish market applica-tion system of the Local 5 Product Line (AXEsoftware). The Tigris are equipped with high-density modem cards, which give the complexa maximum traffic handling capacity of approx-imately 1,320 Erlang (0.1% internal conges-tion). The Tigris are installed in a 2,200 mm BYB501 cabinet using AXE power supply. The Inter-net service provider administers user authen-tication and provides the Internet connection.

For redundancy, the Etheric (simplified ISUPprotocol over TCP/IP) signaling connectionsbetween AXE and Tigris are distributed over twosignaling-terminal-for-open-communication(STOC) subracks. Redundancy is increasedfurther by connecting the Tigris to one anotherby means of serial interfaces. This configura-tion gives AXE secure access to each Tigris.

Ordinarily, traffic is evenly distributed to eachTigris using random routing with mutual over-flow. During maintenance, however, traffic maybe drained from one Tigris using standard AXErouting features.

BOX B, TURKU TELEPHONE LTD.LEADS THE WAY

The media controller, which processes thecall-control functions, provides support forH.323, MGCP and SIP. It will also providethe interface for data calls to the VPSM.When an incoming call is presented to themedia controller, it determines the mediumof the call (data, voice, fax) and initiates theappropriate process. The media controllercan handle one or more media gateways(Tigris), communicating with them bymeans of MGCP. This architecture ensuresscalability and a fault-tolerant approach tosignaling, control, and call connectivity.Figure 4 shows the Tigris VoIP architecturewhen external SS7 gateways and media con-trollers are used.

CapacitiesThe Tigris can support the following ca-pacities:• up to two thousand and one hundred sixty

simultaneous connections;• up to one thousand eighty ISDN

B-channels; or• up to one thousand and one hundred six-

teen 64 K leased lines.

Tigris in the narrowbandworldThe most common application for the Tigrisfamily is as a narrowband gateway into a

broadband IP network. As such, its prima-ry function is to convert modem, fax, ISDNdata or voice into IP packets. In its simplestconfiguration, Tigris is connected via T1 orE1 circuits from the public exchange or cen-tral office and routes incoming trafficthrough the TDM backplane to DSPs andconverts it into packets and IP signals (Fig-ure 5).

This common application is the domainof similar products and provides a stan-dards-based mechanism for connecting toany type of public exchange equipment.However, although this provides an easyconnection mechanism for the serviceprovider, it does have inherent weaknesses.The most important weakness being theunusual traffic load that is created for thepublic exchanges whose calling models aretuned for high call rates but short call-hold-ing times.

The IP world is characterized by low callrates and long call-holding times. Unfor-tunately, this new traffic phenomenon istypically outside of service providers’ con-trol, since in many cases, IP service is pro-vided by an independent ISP and not theservice provider who operates the publicexchange network. The consequences ofthis relationship vary throughout theworld, depending on domestic regulatingand tariffing policies, but in general it

78 Ericsson Review No. 2, 1999

RAS/VoIP gateway with MGC

RAS/VoIP gateway

T1/E1

VoIP Gatekeeper SIP server VPSM AAA/CDR

PSTN IP PSTN

SS7 gateway Media controller IN services

Figure 4Tigris VoIP architecture

Ericsson Review No. 2, 1999 79

causes network congestion and an increasein network growth with little or no offset-ting revenues. Other areas of concern withthis model are• the cost of the T1/E1 ISDN circuits; • the impact of these circuits on the public

exchange control logic; • the impact of unproven SS7 gateways to

the CCITT no. 7 network; and • maintenance and operational aspects of

new equipment.To this end, Ericsson decided that many ofthese problems could be resolved if Tigriswas tightly integrated into the AXE/MSCarchitecture (Figure 6). To achieve this ca-pability, a special development project wasundertaken to design a high-density digitallink (DL2) interface for Tigris that directlyconnects into the AXE/MSC switching fab-ric—the group switch (GS). This approachis unique in the industry, and combinedwith Tigris’s ability to fit seamlessly intoEricsson’s BYB equipment practice, it offersan elegant and extremely cost-effective so-lution for service providers who employAXE/MSC switches or for those who wantto offer proven SS7 gateway capabilities(Box B).

The multi-DL2 interface card is capableof connecting to 16 DL2 interfaces (eachDL2 is the equivalent of one E1). For thesake of redundancy, the card connects to

Voice

Mobile user's modem

Mobile user's cellular

Home office modem/ISDN

Small branch office, Leased-line frame relay

Central office

Switch

Customer n

Customer 1

PSTN/ISDN

IP network

VPSM

Figure 5 Tigris with traditional ISDN PRI networkconnections.

IP network

SS7 signaling network

AXE

16 DL2 links

PSTN network

Figure 6 Tigris integration into AXE/MSC.

planes A and B of the group switch via sep-arate cables. One AXE/MSC can support upto 32 Tigris.

Integration into AXE/MSC can yield sav-ings of 30% compared with traditional net-work connection implementations. Add tothis further savings in floor space, improvedoperational management, and simple inte-gration into the CCITT no. 7 signaling net-work, and service providers gain a very pow-erful solution.

Tigris in a broadbandworldTigris is a natural element for broadbandnetworks. Because it is equipped with ATMcapability, Tigris can be connected directlyinto a packet-based ATM network. Thereare essentially two ways of doing this:• Using the multiprotocol label switching

(MPLS) standard, Tigris connects direct-ly into an equivalent MPLS ATM switch.In this operation, the ATM switch effec-tively functions as a router within the net-

work, just as if another router had beenconnected to Tigris.

• Using the multiprotocol over ATM(MPOA) standard, Tigris effectively pro-vides a virtual connection in an MPOA-based ATM switch. A centralized routerserver provides routing commands toTigris.

Just as Tigris can be integrated intoAXE/MSC, it can also be connected intoEricsson’s next-generation core network,which is based on the AXD 3011 (Figure7). Taken together with the narrowband ar-chitecture, this becomes an extremely pow-erful solution for service providers and arelatively simple migration from legacynetworks toward a packet-based IP net-work.

Tigris in a pure IP worldThe last application with merits for new ser-vice providers entering the market is a pureIP/transmission network (Figure 8). As withpresent-day router networks, this system of-

80 Ericsson Review No. 2, 1999

ATM group switch

Data and voice calls

ATM VPNs

PSTN network

ATM network

Figure 7Tigris in a broadband application.

Ericsson Review No. 2, 1999 81

fers certain benefits. It is, however, a purerouter play that relies on high-speed linksand higher performance.

In this context, Tigris functions as an ac-cess router connecting into massive routingengines, such as the AXI 520. In this model,the network operates like an enterprise net-work, which requires a different form ofmanagement for incumbent serviceproviders while attracting interest from newservice providers entering the market.

ConclusionThe network remains a crucial element. Inan IP world, the ability to offer policy man-agement and quality of service across a net-work is the essence of the new service deliv-

ery model for service providers. Tigris ful-fills this role admirably and supports thetransformation from the circuit-switchedworld to IP.

As a carrier-class product, Tigris has al-ready been recognized as the world’s firstcarrier-class product. Further, old and newservice providers recognize Tigris as an es-sential element in the development of next-generation networks.

Many future developments are underwaywith respect to Ericsson’s IP access solu-tions. Several of these will be based on thesolid foundation of the Tigris architecture.We believe that in the ever-changing worldof communications, stability of the accessplatforms is an essential cornerstone for en-terprise and service providers.

SS7 gatewayMedia controller

High-speed IP router network

Incumbent network

Figure 8Tigris in an IP router network.

1 Blau, S. and Rooth, J.: AXD 301—A new gen-eration ATM switching system. EricssonReview Vol. 75(1998):1, pp. 10–17.

REFERENCES